This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for METHOD FOR CONTROLLING REPEATABLE RUNOUT COMPENSATION ALGORITHM earlier filed in the Korean Industrial Property Office on the 16th of Jan. 1998 and there duly assigned Ser. No. 1122/1998.
1. Technical Field
The present invention relates to a magnetic disk drive and, more particularly, to a method for controlling a repeatable runout (RRO) compensation algorithm in a hard disk drive (HDD).
2. Related Art
For the past several decades, technical improvements in the HDD of computers, together with VLSI (Very Large Scale Integrated circuit) and software techniques, have played an important role in developing the information industry. Disk drives have shown a tendency toward small size and large capacity, and the data recording density of the disk drive has increased by almost 10 times every decade.
In the HDD, data is written on a concentric track formed on any one surface of one or more magnetic recording disks. Theses disks are rotatably mounted on a spindle motor. The data is accessed by a read/write head installed on the arm of an actuator which is rotated by a voice coil motor. The voice coil motor is excited by a current to rotate the actuator and to shift the read/write head. The read/write head is accurately aligned with a storage track on the disk in order to carry out data read and write operations.
An HDD servo controller is constructed such that it may be operated in a track seek mode, a track settling mode, and a track following mode. To raise the data recording density, it is important to reduce track mis-registration (TMR), which is defined as the difference between a track center relative to the width of the track and an actual position of the head. For this reason, a high-precision servo control technique for a head arm in the track following mode has been required.
The HDD is classified as a dedicated servo type or an embedded servo type according to the method of detecting a position error signal (PES). The dedicated servo type detects the PES by using a separate disk in which only position information of the head is written. In the embedded servo type, the position information is written in every sector of the track. Since the dedicated servo type can continuously detect the position information, it has the advantage of providing for design of a controller having a bandwidth larger than that of the embedded servo type. However, an incongruity between a position information disk and a data disk, caused by degradation, results in TMR. Hence, the embedded servo type has widely been used. An existing HDD servo controller for the track following mode has a proportional-integral-differential (PID) structure in which the PES is calculated to compensate for an off-track position of the head by approximating the magnetic head to the track center so as to read and write data. If the track center of the disk coincides with the center of the spindle motor, there will be no repeated component among input following error components when the existing controller is used. Actually, the center of the disk and the center of the spindle motor do not always coincide with each other. A frequency component with a rotating frequency of the disk out of the error components as a basic mode may appear, and an exemplary characteristic curve of the PES is calculated by using a PID control algorithm. Such an incongruity between the center of the spindle motor and the center of the disk leads to an RRO phenomenon.
Recently, it has been discovered that the HDD is easily influenced by the characteristic of its parts due to the high speed and high capacity. The RRO phenomenon may be generated by external damage, such as the rotating frequency of the disk and the supply of similar signals, and a defect in the spindle motor. The RRO phenomenon has a harmful effect on the operation of the drive. Actually, an error occurs by deviation of the PES during the write and read operations of the drive.
RRO compensation algorithms for overcoming the above-mentioned problems have been proposed and applied, and such problems with the drive due to the RRO phenomenon have been improved. The RRO compensation algorithm is generally performed after the power-on ready, initial value setting, head unlatch and calibration modes are sequentially implemented. In more detail, the drive switches from the track seek mode to the track following mode after the calibration modes, and compensates for the RRO phenomenon by using a default table value and an RRO compensation equation having a value updated by the calibration mode as an input parameter. A characteristic curve of the PES is calculated after the RRO compensation algorithm.
However, an RRO compensation mode for performing the RRO compensation algorithm is always enabled when the RRO phenomenon is generated, or even when it is not generated. The RRO compensation algorithm performed upon occurrence of the RRO phenomenon compensates for the RRO phenomenon, which is a good point, but leads to a time delay, which is a bad point. The RRO compensation algorithm, as performed when the RRO phenomenon is not generated, results in a disadvantage, such as a time delay corresponding to the execution time of the RRO compensation algorithm. Furthermore, since the track settling and track following characteristics of the drive become worse, there is also a delay for a steady state response time.
The following patents are considered to be representative of the prior art, and are burdened by the disadvantages set forth herein: U.S. Pat. No. 5,585,976 to Pham., entitled Digital Sector Servo Incorporating Repeatable Run Out Tracking, U.S. Pat. No. 5,550,685 to Drouin, entitled Applying An Adaptive Feed-Forward Algorithm As A Frequency Selective Filter In A Closed Loop Disk Drive Servo System In Order To Compensate For Periodic Perturbations Which Otherwise Appear In The Servo System Position Error Signal, U.S. Pat. No. 5,448,120 to Schaule et al., entitled Integrated Hydrodynamic Bearing/Monitor Assembly, U.S. Pat. No. 5,365,458 to Tamura et al., entitled Motor Eccentricity Measuring Apparatus, U.S. Pat. No. 5,283,491 to Jabbar et al., entitled Air-Bearing Motor Assembly For Magnetic Recording Systems, U.S. Pat. No. 4,734,606 to Hajec, entitled Electric Motor With Ferrofluid Bearing, U.S. Pat. No. 4,616,276 to Workman, entitled Disk File Servo Control System With Fast Reduction Of Repeatable Head Position Error, and U.S. Pat. No. 4,582,461 to Ziegelmeyer, entitled Precision Rotating Tool Mounting Device.
It is, therefore, an object of the present invention to provide a method for controlling an RRO compensation algorithm so as to stabilize a system.
It is another object of the present invention to provide a method for preventing unnecessary time delay upon application of an RRO compensation algorithm.
It is still another object of the present invention to provide a method for preventing a steady state response time delay from being generated by application of an RRO compensation algorithm.
In one aspect of the present invention, a determination is made so as to enable or disable a repeatable runout (RRO) compensation algorithm in a corresponding hard disk drive in a test environment while the drive is being fabricated, and in a user environment, by using a check routine for determining whether to execute the RRO compensation algorithm. A determined result is written on a disk of the drive. When a user utilizes the drive, the RRO compensation algorithm is used or not used according to the determined result.